The present invention relates to a resin-insulated cable such as a flat cable insulated by polytetrafluoroethylene resin and a method for manufacturing the same. More particularly, it relates to a resin-insulated cable in which characters or the like can be printed on the surface of a resin-coated layer to discriminate between cables or to find the positions of the electrical conductors of the cables, and a method for manufacturing the same.
A demand for flat cables each formed of a number of conductor wires arranged in parallel has recently been increased as electronic equipments are developed. Further, a heat resistance has been required in the fiat cables connected between the electronic equipments due to enhancement of the packed density of the electronic equipments. Since the polytetrafluoroethylene resin has a high heat resistance, the reliability of a flat cable including polytetrafluoroethylene resin serving as an insulating material is high. Since the dielectric constant of the polytetrafluoroethylene resin is low, the electrical characteristics of the flat cable are good. Further, the flat cable using the polytetrafluoroethylene resin can have mass termination at the distal end. Such a flat cable has lately attracted considerable attention.
The polytetrafluoroethylene resin is repellent to and non-wettable by water and oil, so it cannot be printed on by a common printing method. When the polytetrafluoroethylene resin is employed as an insulation coating material for flat cables, it is difficult to discriminate between conductors of the cables.
U.S. Pat. No. 2,998,332 discloses a printing method with ink formed by dispersing pigment and fluororesin in the form of colloid in a water solution. Using this ink, printing 10 can be performed as follows. Characters or symbols are written on a predetermined portion of the surface of a flat cable or coloring is applied thereto, and then the ink is attached to the cable by baking. Even though the surface of the polytetrafluoroethylene resin is coated with the ink, the surface repels the ink since its wettability is bad. Since the characters or symbols are printed by the mechanism in which ink is put on the surface of polytetrafluoroethylene, then melted and attached thereto, they may blur. Further, since the ink is suitable for printing straight lines but unsuitable for printing characters, small characters cannot be printed with the ink. Since the ink is fused in a baking process, very small characters, figures or symbols are difficult to print.
U.S. Pat. No. 3,018,188 discloses a technique of printing characters or a like by the hot stamp method in which the surface of ribbon coated with printing composition is transferred to the surface of the cable, using a stamp with a temperature of 327.degree. C. or more. According to the hot stamp method, however, it is almost impossible to print the characters or the like on an uneven surface such as that of a flat cable.